X-ray tube



March 7, 1944. z. i- TL E I 2,343,730.

x-RAY TUBE Filed Nov. 30 1942 INVENTOR.

Patented Mar. 7, 1944 nane X-RAY TUBE Zed J. Atlee, Elmhurst, Ill., assignor to General Electric X-Ray Corporation, Chicago, 111., a corporation of New York Application November 30, 1942, Serial No. 467,333

6 Claims.

This invention relates in general to electronics and particularly to an improvement in X-ray generators.

An important object of the present invention is to provide an X-ray generator for use in the field of superficial therapy providing a more uniform distribution of output; a further object being to provide an X-ray tube having an anode of such construction that it will discharge X- rays more uniformly when used 'as .a. reflection target than has heretofore been obtainable.

One of the difiiculties of obtaining uniformity of X-ray distribution is caused by unequal absorption in the anode. Electrons hitting the target, for example, a target of tungsten, do not stop at the surface of the target but enter the material of the target, with resulting loss in output due to absorption of generated X-rays bythe target material, such absorption being proportional to the distance which an X-ray has to travel through the target material. An important object of this invention is to prevent such loss and improve the efliciency of the tube by shaping the target so as to reduce such absorption and to provide a more uniform intensity of output throughout any unit area of beam; a further object being to provide a target having a surface curved in one plane or spherical.

This invention is not limited in its application to a particular form of tube, but is applicable to tubes of various types of construction. While it relates more especially to the field of tubes in superficial therapy in which low voltage and a stationary anode are used, it may be employed in tubes in which higher voltage is used, or in rotating anode tubes as well as in tubes differing in other respects.

These and other important objects, advantages and inherent functions of the invention will become apparent from the following description, which, in conjunction with the accompanying drawing, discloses a preferred embodiment of the invention. While a preferred embodiment of the inventionis shown and described, it is to be understood that the same is susceptible of modification and change without departing from the spirit of the invention.

The illustrative views shown in the drawing are as follows:

Fig. l is a sectional view through an Xmay generator embodying the present invention;

Fig. 2 is a partial horizontal sectional view taken along the line 2-2 of Fig. 1;

Fig. 3 is a bottom View of a portion of the target shown in Fig. 1;

Fig. 4 is an enlarged partial sectional View of a target of conventional design with the structure of the present invention indicated in dotted lines illustrating the absorption of electrons by the target and the discharge of X-rays;

Fig. 5 is an enlarged sectional View of the target of this invention illustrating the absorption of electrons by the target and the discharge of X-rays; and

Fig. 6 is a sectional view of an alternative form of the invention.

To illustrate the invention there is shown in the drawing an X-ray tube ll comprising an anode l2 and a cathode I3 enclosed in a sealed evacuated envelope M, which may be of any suitable material.

The anode l2 comprises a head supporting a target l5 opposite the cathode in position to receive electrons emitted by the cathode during the operation of the device as an X-ray generator. The cathode It also comprises a head in which a filamentary element It, adapted to be energized as a source of electrons for impingement upon the target l5, may be mounted. The heads of the anode and cathode are supported on stems ii at the opposite ends of the generator, said stems each being supported in an end seal structure forming a hermetic seal between the stems and the ends of the envelope M. The tube H and its constituent parts generally may be of any suitable form. The target end of the anode I2 is preferably curved in one plane as indicated in Fig. l or spherical as indicated in Figs.

, 2 and 6. The target 55, which may be a tungsten button preformed into a convex cup shape before casting into a copper anode in conventional manner, or other suitable material, is provided with a curved surface l8 conforming substantially with the contour of the end of the anode l2, and generally is so formed and arranged as to minimize the path of travel within the material of the target of X-rays generated therein and thereby reduce the absorption of those X-rays by that material incident to such travel. The target is preferably curved, that is, convex in the direction generally of the desired beam; in the case illustrated toward the window l9, which may be of beryllium or other suitable material. The curvature of the outer surface of the target need not extend throughout the entire outer surface of the target, but may be restricted to a given reflection area to produce a desired local spot. An anode having a gold or platinum plating 23 may be employed, as indicated in Fig. 6.

The advantageous character of the construction shown and described will be readily appreciated. In the conventional type of X-ray generator X-rays generated within the target as a result of the impingement of electrons flowing from the cathode upon the target, being subject to absorption Within the target material in proportion to the distance of their travel within that material before emerging therefrom, as shown diagrammatically and in a greatly exaggerated way for purposes of illustration in Fig. 4, in which the outer surface of a target is designated by the letter S, an X-ray X generated within the target would be subject to absorption of variable extent depending upon the direction of its path of travel indicated by dotted lines DI, D2, D3. The differences in length of the portion of these three lines intermediate the point of origin X of the X-ray and the surface 3 of the target is appreciable. The reduction of the length of the path of travel of the X-ray, particularly in the case of the line DI which intersects the surface of the target near its heel and proportionately in the case of the other lines incident to the provision of a target having a curved surface, as above described and designated by the dotted line Y, is apparent. The equalizing effect of curving the outer surface of the target as indicated is shown on an enlarged scale in Fig. 5, in which the dotted lines dl, d2 and d3. representing the distance of travel of an X-ray within the material of a target embodying this invention, are more nearly of equal length and reflect a substantial diminution in the distance of travel of the X-ray within the material of the target, and consequent reduction in absorption. It will be understood that with such equalization of the distance of travel of X-rays within the material of the target, the intensity of the X-ray beam will be more nearly uniform throughout any given unit area of the beam.

Changes may be made in the form, construction and arrangement of the parts without departing from the spirit of the invention, and the right is hereby reserved to make all such changes as fairly fall within the scope of the following claims.

The invention is hereby claimed as follows:

1. An X-ray generator comprising an evacuated envelope, electron emitting means and an anode within said envelope, and a target mounted in said anode, said target being adapted to receive electrons emitted from said means, and a portion of the outer surface of said anode and of said target being convex in one plane, said convex surface forming the reflection area for producing a desired focal spot, whereby X-rays generated in said target will be of substantially uniform intensity in any unit area of the beam.

2. An X-ray generator comprising an evacuated envelope, an anode and electron emitting means within said envelope, a target mounted in said anode and adapted to receive electrons emitted from said means, a portion of the outer surface of said target being convex in one plane, said convex portion forming the reflection area for producing a desired focal spot, whereby the path of travel of X-rays generated in said target toward the outer surface thereof will be minimized.

3. An X-ray generator comprising an evacuated envelope, electron emitting means and an electrode adapted to receive electrons emitted from said means within said envelope, said electrode having its outer surface convex generally in the direction of the desired beam, said convex surface forming the reflection area for producing a desired focal spot and being arranged to minimize the path of travel of X-rays within the electrode, whereby an X-ray beam of substantially uniform intensity in any unit area of said beam may be produced.

4. An X-ray generator comprising an evacuated envelope, a target mounted in said envelope for the generation of X-rays, a portion of the exterior of said target being convex, the convex portion of the target being arranged in the reflection area producing a desire focal spot so as to minimize the path of travel Of X-rays generated in the target, whereby an X-ray beam of substantially uniform intensity in any unit area of said beam may be produced.

5. In an X-ray generator, an electrode for the generation of X-rays having a portion of its exterior convex, the convex portion of the electrode forming the reflection area producing a desired focal spot, whereby the absorption of X-rays generated thereby within the material of said electrode will be minimized and whereby an X-ray beam of substantially uniform intensity in any unit area of said beam may be produced.

6. In an X-ray generator comprising an evacuated envelope, electron emitting means and a target for electrons emitted from said means within said envelope, said target having a portion of its exterior convex in one plane generally 'in the direction of the desired beam, the convex 

